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Table of Content

    15 May 2012, Volume 29 Issue 3
    The Relationship Between Permeable Fractured Zone and Rock Stratum Tensile Deformation
    GAO Yan-Fa, HUANG Wan-Peng, LIU Guo-Lei
    2012, 29(3):  301-306. 
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    To research the relationship between crack stratum’s hydraulic conductivity within permeable fractured zone and tensile deformation of rock stratum, the concept of interlayer stratum was defined first in this paper, then the formula of strata tensile rate ε was deduced, by assuming that two sect of arcs can be used to fit inside and outside brim curve of subsidence trough, and the statistical results of field observation of permeable fractured zone height were obtained at last. The results show that when the tensile rate ε of the interlayer stratum surpasses its deformation limit, the normal tensile crack will be generated, and when ε is larger than the limit rate, the crack stratum will become the hydraulic conductivity stratum. In addition, the layer tensile rate ε depends on layer’s height (h), mining thickness (m), stratum’s subsidence ratio (q), boundary angle (δ0) and full mining angle (ψ), and so on. According to the regression analysis of some coal mine’s permeable fractured zone heights, the harder the upper strata is, the larger the ratio of fractured zone height to mining thickness(H-T ratio)is, and the smaller the layer tensile rate of top stratum within water flowing fractured zone is.
    Mechanical Model of Stability of Water-Resistant Strata Under Mining and Its Application
    YAO Bang-Hua, BAI Hai-Bo, HUANG Han-Fu
    2012, 29(3):  307-311. 
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    In this paper, to research the stability of overlying water-resistant strata and prevent the roof water inrush accidents as well as implement water-preserved-mining, we regarded the water-resistant strata composed by only one rock stratum as clamped rectangular thick plate on foundation, and took the support effect of broken rock mass under the water-resistant strata into account, then deduced the deflection and stress expression according to energy method, and obtained the stress distribution characteristics of overlying water-resistant strata, as well as the variation rule of critical load along with working face advancement. In addition, combined with specific engineering practice, the stability of overlying water-resistant strata was analyzed by numerical simulation. The results indicate that: 1) after coal seam mining, the stress of overlying strata reaches the maximum value in the middle of longer boundary of the plate, where the rock is easy to be damaged; 2) the supporting effect of broken rock mass have important influence on the stability of overlying water-resistant strata, that is, the thinner the mining thickness is, the stronger the supporting effect of broken rock mass to the overlying water-resistant strata is, and the more difficult the water-resistant strata to be broken. The research results can provide some reference for the prevention of roof water inrush and water-preserved-mining practice.
    Influence Factors of Solid Material Particles Motion in the Feeding System of Fully Mechanized Coal Mining and Backfilling
    ZHANG Ji-Xiong, AN Bai-Fu, JU Feng
    2012, 29(3):  312-316. 
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    In this paper, based on the solid material particle’s differential motion equations (displacement, velocity, acceleration) in the pipeline of fully mechanized coal mining and backfilling, the particle diameter and density of the solid material are established as the main factors which affect its motion. In addition, the effect characteristics of the two main factors to the particle motions are studied by theoretical analysis and MATLAB software. The results indicate that the solid material particle experiences a varying acceleration motion in the feeding pipeline, and the total acceleration time increase as the particle diameter and density increase. According to the engineering conditions of No. 12 coal mine of Pingdingshan Coal Group, the proper diameter of the used solid material particle should be 80 mm, the feeding system has not been blocked heretofore, and the real feeding rate can reach to 500 t/h.
    Research on Filling Repeated Mining Technology in Small Pit Goaf in Extremely Thick Coal Seam and Its Application
    ZHOU Bao-Jing, XU Jin-Hai, WU Rui
    2012, 29(3):  317-321. 
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    To ensure normal advance and safe mining of working face containing small pit goaf, the technology of filling with repeated mining is introduced in this paper, that is, the inorganic materials are used to fill the small pit goaf first, which can form a cutting layer or key bearing layer inner the small pit goaf according to the position relation between the working face and goaf, and makes that it can maintain the stabilities of face roof and surrounding rock when the face passing through the small pit goaf. Then, the normal fully mechanized caving face is arranged for mining. In the paper, based on the mechanics structure of key bearing layer in small pit goaf during the process of repeated mining, and the mechanics model of weight drop and low speed impingement plate structure, we conducted systematic analysis on the mechanism of grouting filling in small pit goaf and the stability of regenerated key strata in the filled area of small pit by using mechanism analysis and theoretical calculation, and figured out the intension and thickness parameters of key bearing layer for maintaining the stability of face roof and surrounding rock around coal wall. The results show that applying the technology of grouting filling in layers to build key bearing layers in a certain thickness can maintain the stability of roof and coal wall areas when the working face mining through the small pit goaf.
    Study on Upward Mining of Sublevels for Gob-side Entry Retaining in Three-soft Thin Coal Seam Group
    CAO Shu-Gang, ZOU De-Jun, BAI Yan-Jie
    2012, 29(3):  322-327. 
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    In this paper, to investigate the influence of different mining sequence of sublevels on gateways in conditions of gob-side entry retaining in three-soft thin coal seam group, we carried out numerical simulation study on the upward and downward mining sequences of sublevels respectively in the three-soft thin coal seam group with ultra-close distance in one coal mine of Southern Sichuan, based on the previous field investigation and analysis, shield supporting study and experimental determination of rock mechanics parameters. The results show that extrusion and shear failures are occurred easily in the roadway roof and roof of higher side when the downward mining sequence of sublevels is used, and the rock packing of higher side has poor stability, while the vertical stress and shear stress of lower side in the range of 0.5m decrease 1 MPa at least during upward mining, compared with the former mining sequence, and the produced horizontal stress can prevent the rock packing of lower side slip towards the gob side, which is beneficial to increase the initial strength of the rock packing.
    Nondestructive Testing Principle and Technology of Hydraulic Supports by Ultrasonic Phased Array in Top Coal Caving Face
    YIN Shuai-Feng, HE Fu-Lian
    2012, 29(3):  328-333. 
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    ased on the necessity of nondestructive testing of hydraulic supports in top coal caving face, the nondestructive testing technology of one-dimensional ultrasonic phased array was proposed in this paper, to accurately inspect the large-scale electromechanical equipment and its components with relatively complex geometric figures. According to the mobile column detection of ZFG10000/23/37H hydraulic supports, the basic principles of phase-controlled focus and phase delay was conducted. Combined with the normalized acoustic pressure function of single element, the significance of sine gain weighted apodization technology was analyzed when applied into reducing the definition of output waveform influenced by sidelobe. Finally, in view of the detection of weld cracking shields at 5201 working face in Wujiagou coalmine, the composition and testing process of nondestructive detection were illuminated. The application examples indicate that the internal micro-fractures and surface interpenetrated fractures of shields can be accurately quantified and located by nondestructive testing technology of one-dimensional ultrasonic phased array, and the development direction and interpenetrated tendency of the fractures can be also exactly judged, according to the results of three-dimensional imaging output.
    Analysis on Evolution Laws of Floor Burst Induced by Dynamic Disturbance
    XU Xue-Feng, DOU Lin-Ming, LIU Jun
    2012, 29(3):  334-338. 
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    To research the evolution laws of floor burst under dynamic loads, theory analysis and numerical simulation methods were used in this paper, to study the response characteristics of stress, displacement, et al, of roadway bottom coal under dynamic disturbance, and to reveal the causing reason and burst process induced by dynamic stress. The results show that the buckling failure and deformation will happen in the bottom coal seam, when the superposition of dynamic stress and high horizontal stress in floor reaches or surpasses the strength limit. In addition, the tensile stress, which is formed by the reflection of incident stress wave at the floor surface, causes spallation damage in the floor, and with the gradual enlargement of the damage range, the floor burst will be induced. Under the dynamic loading, the horizontal stress, vertical stress and stress difference firstly increase in a small extent, and then decrease substantially. At the same time, the scope of tensile failure zone and the vertical displacement increase subsequently. During the process, the concentration of horizontal stress in floor disappears gradually.
    Study on Forced Roof Caving to Hard Roof by Deep-hole Pre-blasting in Shallow Coal Seam
    ZHANG Jie
    2012, 29(3):  339-343. 
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    Overlying strata in Sheng-Fu mining area belong to inferior hard roof.Because of the shallow burial depth and thick layered of main roof, it needs to avoid the large area caving of the main roof during the first weighting period of working face. In this paper, based on the different physical simulation experiments, the failure mechanism of main roof is discussed when blasting is used. In addition, the mechanical model of main roof failure is established, and the relationship between the first weighting step of main roof and the depth of blasting hole is deduced. Thus, the first weighting steps of main roof in Nanliang coal mine are calculated according to different explosion parameters. The parameters which are determined by experimental and theoretical studies have achieved good application results in field testing, which can provide reliable theoretical basis for determining the explosive parameters in implementing forced roof caving by deep-hole pre-blasting.
    Strata Behavior of Fully-Mechanized Face with 7.0 m Height Support
    JU Jin-Feng, XU Jia-Lin, ZHU Wei-Bing
    2012, 29(3):  344-350. 
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    Based on the measured results of ground pressure in No. 22303 working face of Bulianta Coal Mine, Shendong mining area, the strata behaviors in different stages of the first 7.0m height fully-mechanized face around the world are summarized in this paper, and combining with the strata behaviors in various fully-mechanized faces of Shendong mining area, the differences of various fully-mechanized faces are comparatively analyzed in detail. The results show that the strata behavior of 7.0 m support fully-mechanized face remains regular when mining under the overlying coal pillars, but when nearly mining out of the pillar area, the coal wall caves, largely which directly leads to the crushing death of the scraper conveyor. While mining under the long wall goaf, the strata behavior of single key stratum structure in 7.0 m fully-mechanized face differs from that in double key strata structure. Within the single key stratum structure, the nearer the key stratum structure to the coal seam is, the larger the parameters of strata behavior are (except the roof weighting step), while within the double key strata structure, the roof weighting step and dynamic load coefficient present periodical alternating changes, and the large roof weighting step comes along with the small dynamic load coefficient. Through comparing the strata behaviors between 7.0 m fully-mechanized face and several other fully-mechanized faces in Shendong mining area, we conclude that the higher the mining height is, the larger the support strength is, and the smaller the dynamic load coefficient is. In addition, the higher the mining height is, and the nearer the first inferior key strata to the coal seam is, it is more easier to form “cantilever” structure in the first inferior key strata, so as to lengthen the roof weighting.
    Control Principle and Technology of Final Compression Ratio of Backfilling Materials
    ZHOU Yue-Jin, CHEN Yong, ZHANG Ji-Xiong
    2012, 29(3):  351-357. 
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     In this paper, to evaluate the goaf backfilling effectiveness with solid wastes, the final compression ratio of backfilling materials was proposed as the technical measurement index, and the associated key affected factors were also analyzed. The results show that the three key affected factors of compression ratio include the roof subsidence before backfilling, the gap between the backfilling body and roof, and the compression amount of filling materials. Hereby, to improve the final compression ratio of backfilling materials obviously, the structures and the parameters of filling equipment were optimized, the filling technology was upgraded, and the supervisory control system of compression ratio was also established. The above achievements have been successfully applied in No.12 mine of Pingdingshan coal group. The application results show that the actual final compression ratio of backfilling materials in the goaf is up to 89.4% and the maximum surface subsidence is merely 15 mm, thus ensuring the safety of surface buildings.
    Mechanics Analysis on the Stability of Key Block in the Gob-side Entry Retaining and Engineering Application
    LI Ying-Fu, HUA Xin-Zhu, CAI Rui-Chun
    2012, 29(3):  357-364. 
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    Due to the low bearing capacity of roadside backfill in the early stage of roadside backfilling, it is critical to maintain the stability of key block at the face end during roadside backfilling. In this paper, based on the criterions of slip instability and rotation instability, the formula of roadside support resistance is derived, through establishing the mechanical model of key block structure in the gob-side entry retaining. Taking headentry of No.512(5) mining face as project background, we have studied the effects of roadside coal support resistance, roadway-inside support resistance, roadside support resistance and width of roadside backfill on the stability of key block. The results show that it is beneficial to improve the stability of key block, when using high active supporting force in roadway-inside support, high pre-stressed, high-strength bolting in roadside coal support, and adopting the backfilling materials with high strength and quickly increased resistance at early stage in roadside support. Based on the study results mentioned above, the supporting parameters of gob-side entry retaining in the headentry of No.512(5) face are designed. The engineering practices show that, it is reasonable and feasible to adopt combined support with bolting, cable and wire mesh as the basic supporting in roadway-inside, use different strengthening supporting in different zones of roadway-inside, and choose backfilling process system of pumping quick-setting materials of high water in roadside supporting. The stability of key block during the gob-side entry retaining can be ensured when the support resistances of roadway-inside and roadside are not less than 0.15 MPa and 3.5 MPa, respectively, with the width of roadside backfill is 2.5 m.
    Study on Stress Distribution Law in Anchoring Section of Prestressed Bolt
    ZHENG Xi-Gui, ZHANG Nong, XUE Fei
    2012, 29(3):  365-370. 
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    To reveal the pre-stressed anchor mechanism and optimize the supporting parameters of surrounding rock, the stress of the anchor and surrounding rock system was analyzed in this paper, and the expressions of shear and compressive stress distribution in surrounding rock under the elastic state were obtained. By using MATLAB, the pre-stress distributions in the rod body and surrounding rock under different conditions were calculated, such as different anchoring methods, surrounding rock properties, bolt diameters and pre-tightened forces. The results show that, under different anchoring methods, the distribution forms of pre-stresses are basically the same, but the action spheres are different. The lengthening of bolting method can increase the sphere of pre-stress, and the effect of pre-stressed anchor in the soft rock is better than that in hard rock. The increase of anchor diameter can improve the diffusion effect of sticky anchor force in the surrounding rock, while the increase of the pre-tightened force can’t change the pre-stressed diffusion range in anchored section, but can improve its peak stress, and improve the compressive stress of surrounding rock near orifice as well, which has efficient improvement effect of stress state on the surface of surrounding rock.
    Development and Application of Anchor Dynamometer in Similar Simulation Experiment
    WU Yong-Ping, WANG Jun-Chao, JIE Pan-Shi
    2012, 29(3):  371-375. 
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     To make better real-time observation on the anchor's stress in different positions of roadway, the roadway similar material model can be used to analyze the deformation and failure mechanism of surrounding rock, and provide scientific basis to determine reasonable support parameters of roadway. In this paper, a new type of stress sensor was designed by using LY-12 duralumin alloy as elastic material. By contrast analysis of disadvantages of present anchor dynamometers, the sizes of whole-bridge ring anchor dynamometer in no-hole status was determined by using material mechanics theory. In addition, the stress distributions of anchor dynamometer in the statuses of no-hole and with a hole were contrast analyzed through the numerical calculation model built by FLAC3D. The experiment calibration and application results show that the structure size, stability and accuracy, et al of the new dynamometer are all appropriate for the requirements of similar material simulation experiment, which can provide an impactful means for testing anchor stress in similar material simulation experiment, and has wide prospect of application.
    Study on Long-Term Stress and Deformation Characteristics of Strip Pillar
    CHEN Shao-Jie, ZHOU Hui, GUO Wei-Jia
    2012, 29(3):  376-380. 
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    To study the long-term stress and deformation states of strip pillar, the strip pillars in Daizhuang coal mine were monitored with borehole stress-meters and displacement monitors for a long time. The study results show that the strip pillar of 70 m in width can be divided into 58 m elastic zone,4~5 m plastic failure zone and 1 m fully broken zone. The actual support ability of each zone is determined based on the correction of measured data, for example, the actual long-term support ability of the strip pillar in depth of 5 m is around 11.896 MPa, while the average long-term support ability of the intermediate part of 50 m in width is 29.5 MPa, and the bearing capacity of pillar is greater than the weight of overlying strata within the mining and reservation width. Meanwhile, the goaf is filled by the falling gangue, which can certainly play a role in supporting the roof and overlying strata, so the strip pillar can keep stable for a long time.
    Numerical Simulation of Bolted Roadway Based on Composite Material Mechanics
    LIU Xi-Liang, LIU Hong-Yu, HAN Xian-Jun
    2012, 29(3):  381-385. 
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    To establish a simplified equivalent method accorded with the stability analysis of surrounding rock and support parameters evaluation in the bolt-shotcrete support, a mechanics model of composite materials for anchored rock mass is established in this paper, according to the basic principle of composite material mechanics. First, regarding the anchor and mortar as elastic body, the elastic parameters of equivalent anchor-mortar mechanical model are deduced. Then, regarding the rock and anchor-mortar complex as composite reinforced materials, the transverse isotropic body model is established, and the defined formula of corresponding parameters from the equivalent mechanical model are deduced. Moreover, based on the engineering example, numerical simulations are conducted to study the composite roadway model and conventional discrete roadway model. After the comparative analysis about the displacements in two sides, top and bottom of roadway and surrounding rock stress, the feasibility and applicability of the equivalent method is verified.
    Study on Mining Scheme and Surface Railway Safety in Meng Jia-gang Iron Mine
    LI Hai-Zhou, YANG Tian-Hong, CHEN Shi-Kuo
    2012, 29(3):  386-390. 
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    According to the geological condition in Mengjiagang Iron mine, as well as railway, highway passing through the mining area, in order to maximize the resource recycling and ensure the transportation safety of upper railway, two mining schemes including the cemented filling method and room and pillar method were adopt in this paper. Mechanical parameters of rock mass were comprehensively determined based on rock macrostructure survey, sampling, rock mechanics test and engineering analogy. In addition, the software of Comsol Multiphysics was used to calculate the surface sedimentation height caused by the two different mining schemes. The numerical calculation results show that when using cemented filling mining method with the mix proportion scheme of “tailing + cement + fly ash + water”,  the sedimentation values of railway surface in the range of No. 5 and No. 6 exploration lines are all less than 30 mm, which meets the requirement of safety regulations, and will not affect the normal operation of railway on the surface. The validity of cemented filling method with tailings is verified well by later surface displacement monitoring results.
    Analytical Calculation on Temperature Field of Tunnels in Cold Region by Laplace Integral Transform
    FENG Qiang, JIANG Bin-Song
    2012, 29(3):  391-395. 
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    The low temperature in cold region is quite harmful for the tunnels which are excavating or have been excavated. Therefore, the study on temperature field distribution of tunnel can play an important role in frost damage prevention. In view of this problem, an analytical model was established, and Laplace transform method was adopted to develop the analytical method of temperature field on tunnel. By means of transformation, the problem was transformed from time domain to Laplace domain; and the solution in Laplace domain was obtained, then the solution in Laplace domain was inverse transformed to that in time domain. Because the solution in time domain is difficult for actual calculation, it is necessary to carry on numerical inversion for the solution in Laplace domain by stehfest inversion method, to obtain the numerical solution in time domain. By error checking of stehfest method, it is obtained that when the cycle series N = 18, the error is about 10-5~10-7, suggesting that the method is reliable. Finally, based on the example checking of Fenghuo Mountain tunnel, the result obtained is identical with actual design, thus providing theory basis and calculation method for engineering design in cold region.
    Study on Warning Criterion of Critical Separation Area for Separation Type Roof Accident
    XIE Jian-Lin, XU Jia-Lin, ZHU Wei-Bing
    2012, 29(3):  396-399. 
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     In order to better control and avoid the roof accidents, we put forward the roof accident prevention and control system of “roof caving mechanism-roof control design- roof support quality and dynamic monitoring-roof accident warning” in this paper. In addition,  taking separation type roof accident as research object, considering the roof as isotropic body, and simplifying the movement and destruction of strata as simply supported beam, we deduced the calculation formula for critical separation area Smax of roof breakage according to the deflection curve equation of simply supported beam, and proposed Smax as the warning criterion of separation type roof accident. Through the engineering example analysis, the accuracy of Smax warning criterion for separation type roof accident is verified.
    Evolution Law of the Structure and Permeability for Coal Under Solid-Liquid Coupling
    CHENG Qing-Ying, HUANG Bing-Xiang, LI Zeng-Hua
    2012, 29(3):  400-406. 
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    To investigate the structure transformation and permeability evolution law of coal seam under the effect of solid-liquid coupling and seepage water pressure (hydraulic gradient), the permeability test of coal during the overall stress-strain process has been carried out on MTS 815.02 electro-hydraulic servo rock mechanics test system with the method of transient pressure pulse. The test results show that the coal permeability is closely related to its internal structure, and the permeability evolution is consistent with its variation tendency of internal fractures in the overall stress-strain process. When the strain softening is 24.98 percent of the peak strength, the coal permeability reaches to 15.69×10-13cm/s, which is 79.30 and 16.34 times of that in elastic stage and peak value, respectively. When the solid-liquid coupling doesn’t produce damage, the transient permeability coefficient is proportional to hydraulic gradient on the whole, and the seepage water pressure can cause dislocation and closure to structural planes or make rupture debris gather and block up seepage channel. After the deformation of coal sample enters into elastic-plastic stage, the transient permeability coefficient first decreases with time on the whole and increases rapidly to a certain peak value after it decreases to a certain value, then, it gradually decreases again and tends to be stable. In addition, when the coal sample goes from elas-tic-plastic stage, plastic stage to failure (residual strength) stage, the difference between the mutations peak and initial transient permeability coefficient becomes smaller and smaller, and the emergence of middle mutations peak needs longer and longer time. Moreover, by using transient pressure pulse method to measure and evaluate the rock permeability, the data should be adopted when the upper and lower water pressure difference becomes stable at the first time, to calculate the permeability.
    Study on AE Variation of Sandstone Brittle Failure Based on Strain Level
    SUN Qiang, XUE Lei, QIAN Hai-Tao
    2012, 29(3):  407-410. 
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     AE information of rock brittle failure is closely related to the deformation failure process under loading, and AE will increase suddenly in the stages of expansion point before rock rupture, stress peak point, and inflection point after the peak value, respectively. In this paper, based on three-dimensional renormalization group theory, the ratio expression between the strain related to the expansion point before rock rupture and the one related to the stress peak point is obtained, and the critical ratio has a range of 74% to78% under the uniaxial loading, which has been proved by the rigid loading test of sandstone. Meanwhile, according to the analysis of test data, the strain value between the expansion point before rock rupture, stress peak point, and inflection point after peak value is nearly stable.
    Research on Outburst Prevention Technology of High Pressure Hydraulic-Cutting Seam Through Layer and Its Application
    ZHANG Jian-Guo, LIN Bai-Quan, DI Cheng
    2012, 29(3):  411-415. 
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    In this paper, in order to resolve the problem of gas and coal outburst in the drilling process of coal seam with high concentration of gas and low permeability, the gas-outburst prevention technology of high pressure hydraulic-cutting seam through layer was developed, which is integrated by drilling and seam cutting. Numerical simulation method was used to compare the pressure relief effects of borehole drilling and high pressure hydraulic-cutting seam. The results show that the pressure relief effect of high pressure hydraulic-cutting seam is much better than that of seam drilling. The cutting slit has broken the “bottleneck effect” around the drilling hole, and the extension of fractures and weak planes in coal mass is transformed into interlaced transfixion fracture network, which increases the permeability of coal mass and promotes the gas release. Industrial experiments indicate that compared with general method of coal seam drilling, the high pressure hydraulic-cutting seam through layer produces a better effect of pressure relieving and permeability improving, while the flow of drilling gas extraction and disturbance volume of coal mass have increased substantially, which improves the gas extraction efficiency.
    Attribute Synthetic Evaluation Model for Predicting Risk of Coal and Gas Outburst
    MA Yan-Kun, WANG 恩Yuan, LIU Zhen-Tang
    2012, 29(3):  416-420. 
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    Based on attribute mathematics theory, we propose an attribute synthetic evaluation model for predicting the risk of coal and gas outburst in this paper. Six indexes are chosen to evaluate coal and gas outburst in the model, including the gas pressure of coal seam, the initial speed of methane diffusion, the firmness coefficient, types of the coal damage, comprehensive index of D and K. The attribute measurement functions of each index are constructed based on the attribute mathematics theory, while the calculation methods of the single index attribute measurement and comprehensive attribute measurement are provided, respectively. Meanwhile, the weight of each index is given with the method of similarity figure and similarity weight, while the evaluation results are determined by the reliability code. According to the application results of the model in some coal mines in Pan County, Guizhou province, the evaluation results are basically consistent with the actual situation, which is proved that the evaluation model can be used in outburst prediction.
    Influential Effect on Spontaneous Combustion of Float Coal Induced by Gas Extraction in Upper Roadway
    CHU Ting-Xiang, LIU Chun-Sheng, YU Ming-Gao
    2012, 29(3):  421-428. 
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    In this paper, based on the gas extraction technique of upper roadway in high gas and easily spontaneous combustion coal seam, taking the study of spontaneous combustion mechanism as point of penetration, according to the actual spontaneous combustion situation of LW13190 in Gengcun coal mine, Yima coal industry group, we have studied the strata fracture development, air leakage passage model, expansion property of float coal in goaf, and power source of air leakage, et al, by using theoretical analysis, mathematical model and field aided test. The results show that the gas extraction in upper roadway has increased the spontaneous combustion risk in the high gas and easily spontaneous combustion coal seam, ,which mainly embodies in: 1) Air leakage passage and power are exist in the port between the coal face, goaf and upper drainage roadway; 2) The coal- rock mass fractures are fully development duo to mining stress and loose circle of drainage roadway, while the compaction degree of float coal in goaf decreases, and the expansion property of float coal increases, which are beneficial to the spontaneous combustion and heat storing of coal mass; 3) Once the float coal in goaf is oxidized, the temperature gradient will exit between the high temperature dot in goaf and air leakage passage. Then, the formed endogenous fire pressure will exacerbate the spontaneous process of broken float coal in goaf, and induce the spontaneous combustion of float coal.
    Numerical Simulation on Mine Gas Explosion in Different Gas Content
    CHEN Xian-Feng, ZHANG Yin, XU Xiao-Jiang
    2012, 29(3):  429-433. 
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    In this paper, to research the propagation rule and inherent mechanism of premixed flame in pipeline, we established the mathematical model and physical model by using numerical simulation method, and conducted simulation research on the process of mine gas explosion in different gas content. The calculation results show that both the velocity and pressure in gas explosion process experience the stages of “rise - fall - second wave - fall - swing”. In the initial stage of the flame propagation, the deflagration volume of gas increases rapidly, and the velocity, pressure and temperature of the flame also rise up quickly, and present laminar burning state during a certain time. Then, both the velocity and pressure have appeared swings in various degrees, which are the results of concurrent effects of pressure wave and reflected wave. Meanwhile, the velocity of the flame achieves the peak value ahead the pressure, this is mainly attributed to the superimposition of explosion pressure wave and reflected pressure wave, which leads to the rise of pressure, while the reflected pressure wave leads to the decrease of ve-locity. The best content of mine gas is that the velocity and pressure are in the minimum value, and the gas burning lasts the longest time, in this time the mine gas hasn’t been completely accelerated, and haven’t formed the detonation state.
    One-Dimensional Numerical Simulation of Thermal Reverse-Flow Oxidation of Ventilation Air Methane in Coal Mine
    WANG Peng-Fei, FENG Tao, HAO Xiao-Li
    2012, 29(3):  434-439. 
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    In this paper, an one-dimensional mathematical mode was set up, to investigate the thermal reverse-flow oxidation of ventilation air methane (VAM) in coal mine, and Fluent software was adopted to simulate the effects of the thermal structures of oxidation bed and the operating condition parameters on the thermal structure, oxidation ratio of methane and outlet temperature. The results indicate that: 1) The temperature field of oxidation bed presents trapezium distribution, and the high-temperature zone makes reciprocating movement periodically along the height direction of oxidation bed. 2) With the increase of methane concentration, the high-temperature zone widens, and the maximum temperature and the outlet temperature increase accordingly, while the oxidation ratio of methane increases slightly. 3) As the ventilation air volume increases, the peak temperature, reaction rate and outlet temperature all rise significantly, the reaction zone moves towards both ends of the oxidation bed, and the high-temperature zone widens, while the oxidation ratio of methane decreases. 4) With the extension of half cycle, the reaction zone and high-temperature zone move towards the center of oxidation bed, the
    high-temperature zone narrows down, the outlet temperature increases, and the oxidation ratio of methane decreases slightly. 5) With the continuous increase of heat loss on wall, the peak temperature, the temperature in high-temperature zone, and the oxidation ratio of methane gas all decrease, the reaction rate also falls sharply, while the high-temperature zone narrows down distinctly.
    Experimental Investigation on Suppression of Gas Explosion with Water Mist
    BI Ming-Shu, LI Zheng, ZHANG Peng-Peng
    2012, 29(3):  440-443. 
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    In this paper, the suppression of gas explosion by water mist was experimented in a closed vessel of 68 mm in diameter and 1 200 mm in length, and the effects of different amount of water mist on the maximum gas explosion pressure and the maximum pressure increase rate were analyzed. The results show that the maximum gas explosion pressure and maximum pressure increase rate increase, and the time of explosion pressure reaching the peak value decreases, at the situation of a small amount of water mist. With the increase of the amount of water mist, the maximum explosion pressure and maximum pressure increase rate decrease, and then the time of explosion pressure achieving at the peak value increases. This shows that a large amount of water mist may have more obvious influence on gas explosion.
    Stability Evaluation and Monitoring System of A Shaft in Jinchuan No. Mine Area
    LIU Zeng-Hui, GAO Qian, GUO Hui-Gao
    2012, 29(3):  444-450. 
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    After analysis of the shaft damage reasons, the different reinforcement measures and the corresponding construction plan have been taken for the engineering characteristics of different rock segments. The influence of mining underground to the shaft repaired has been studied by establishing a numerical model in the identical condition of reinforcement measures, the corresponding geological conditions and mining order. The Numerical simulation experimental results showed that the shaft is a certain degree damage risk with the deeper mining. According to the engineering distribution between the shaft and ore bodies, the distributed optical fiber sensing technology has established a dynamic monitoring system for long-term monitoring and predicting rock mass deformation accurately.